The project was supported by the National Natural Science Foundation of China (51071138), Natural Science Foundation of Hebei Province, China (A2010002048), and Science Foundation of Yanshan University for the Excellent Ph. D. Students, China (YSUSF201102).

To understand the experimental observation that the dynamic parameters determined for enthalpy and dielectric relaxation might differ in fragile glass-forming molecular liquids, a fragile molecular liquid, triacetin, was chosen for the study of the two relaxation dynamics. The non-Arrhenius and nonexponential characters were focused, and the kinetic fragility and non-exponential parameter determined from the two relaxation measurements were found to be remarkably similar. Experimental results indicate that the degree of correlation in the molecular motions involved in the two relaxations depends on molecular flexibility. The dependence of the dynamic parameters on molecular structures in the glass forming liquids is discussed.